Intelligence and Miscellaneous Articles. 239 



than the zones of diminishing radius it successively meets; it thus 

 describes a sort of spiral, through the composition of its own velo- 

 city with that of the parallels over which it flows. A similar devia- 

 tion of the equatorial current towards the poles is also observed 

 upon the eastern coasts of Africa and of Asia ; so that in general we 

 may say that in the rotation of the globe the waters of the equato- 

 rial regions tend to lag behind, and are in consequence deflected by 

 the eastern coasts and impelled towards the poles. This flow of the 

 waters towards the poles gives rise to counter-currents which restore 

 them again to the equatorial zones. 



If the superficial temperature of the globe were everywhere uni- 

 form, and if there were no friction between the waters and the earth, 

 nor between portions of water moving with different velocities, this 

 circulation, once begun, would last for ever, the globe would lose a 

 certain quantity of mechanical work through the effort of the equa- 

 torial coasts, which would be communicated to the waters in the 

 act of imparting to them the earth's velocity ; but, on the other 

 hand, the waters, being impelled upon the western coasts moving 

 with a less velocity as their distance from the equator increases, 

 would communicate to those coasts its acquired impetus, thus resto- 

 ring the^work expended upon them by the eastern coasts towards the 

 equator. A continual interchange of force would thus be taking 

 place between the solid globe and the waters on its surface ; but in 

 the supposed circumstances the compensation would be perfect, so 

 that the general routine of the phenomena would remain constant. 



But friction does in reality act in the phenomena, and consequently 

 the compensation cannot be complete ; the waters having lost 

 through friction a part of the work which they contained, cannot 

 restore entirely the force they absorbed in acquiring increased ve- 

 locity ; the equatorial current will therefore be retarded ; conse- 

 quently a greater expenditure of work will be required to impel it 

 forwards, so that the motion of the whole system will gradually 

 diminish, the force stored up in it being at length expended in fric- 

 tion. To maintain the motion of the currents and of the globe un- 

 impaired, it is necessary that some exterior source of work be con- 

 stantly in action capable of compensating that power which is changed 

 through friction into heat or other forms Gf energy. 



The temperature of the waters in the vicinity of the equator is 

 always higher than that of the waters of the polar regions, for the 

 reason that the sun's rays fall more copiously, surface for surface, 

 towards the equator. The currents which flow towards the poles 

 are therefore continually cooled, and those which return to the 

 equator are continually heated ; it follows that the waters flowing 

 towards the poles gradually shrink in bulk, and that those which are 

 returning gradually expand. As was stated above, if the tempera- 

 ture were uniform over the whole surface, there would be a perfect 

 balance between the power abstracted by the currents in the vicinity 

 of the equator and that restored by them in moving towards the 

 poles (always supposing there were no friction); but the local differ- 

 ences of temperature give rise to notable effects. When the waters 

 from the poles flow towards the equator, they not only slacken their 



